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Fragmenting a heap is something I haven’t worried about for years. When you allocate and deallocate memory in certain patterns you can leave areas of unallocated memory stranded inamongst allocated memory. This can lead to the situation where you have, say, 10Mb of memory free, but yet an allocation for 256 bytes fails as although you have all this free memory, none if it is in a big enough continuous lump to give you your 256 bytes.

http://xania.org/200512/crt-heap-fragmentation-in-windows

2. Low-fragmentation heap definition

The LFH is not a separate heap. Instead, it is a policy that applications can enable for their heaps. When the LFH is enabled, the system allocates memory in certain predetermined sizes. When an application requests a memory allocation from a heap that has the LFH enabled, the system allocates the smallest block of memory that is large enough to contain the requested size. The system does not use the LFH for allocations larger than 16 KB, whether or not the LFH is enabled.

Applications that benefit most from the LFH are multi-threaded applications that allocate memory frequently and use a variety of allocation sizes under 16 KB. However, not all applications benefit from the LFH. To assess the effects of enabling the LFH in your application, use performance profiling data.

http://msdn.microsoft.com/en-us/library/aa366750%28VS.85%29.aspx

3. What is the cause of fragmentation

Imagine, for concreteness, a program that allocates memory in a loop like this:

* p1 = alloc(128)
* p2 = alloc(128)
* free(p1)
* p3 = alloc(96)
* (Keep p2 and p3 allocated.)
* Repeat

Under the classical model, when the request for 96 bytes comes in, the memory manager sees that 128-byte block (formerly known as p1) and splits it into two parts, a 96-byte block and a 32-byte block. The 96-byte block becomes block p3, and the 32-byte block sits around waiting for somebody to ask for 32 bytes (which never happens).

http://blogs.msdn.com/b/oldnewthing/archive/2010/04/29/10004218.aspx?PageIndex=2

4. Low-fragmentation heap in Visual Studio 2010 and Windows Vista/7

Generally speaking, the low-fragmentation heap works pretty well for most classes of applications, and you should consider using it. (In fact, I'm told that the C runtime libraries have converted the default C runtime heap to be a low-fragmentation heap starting in Visual Studio 2010.)

http://blogs.msdn.com/b/oldnewthing/archive/2010/04/29/10004218.aspx

Starting with Windows Vista, the system uses the low-fragmentation heap (LFH) as needed to service memory allocation requests. Applications do not need to enable the LFH for their heaps.

http://msdn.microsoft.com/en-us/library/aa366750%28VS.85%29.aspx

http://www.89teen.com

Why the low fragmentation heap (LFH) mechanism may be disabled on some computers that are running Windows Server 2003, Windows XP, or Windows 2000
http://support.microsoft.com/kb/929136

Chris Valasek, Understanding the Low-Fragmentation Heap: From Allocation to Exploitation
http://www.blackhat.com/html/bh-us-10/bh-us-10-briefings.html#Valasek
http://illmatics.com/Understanding_the_LFH.pdf

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Czytaj dalej wpis Heap fragmentation and Low-fragmentation Heap
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Standing on the shoulders of the blue monster - Hardening Windows applications

published by Kuling on wt., 2010-08-10 13:28

Cytat:

Microsoft has implemented lots of useful functionality in Windows that they use in their own products. Many of these features can be used to enhance the security of third party applications, but not many developers or software architects know about them. This talk will detail some of the technical underpinnings of Windows features like UAC, IE protected mode and Terminal Serivces and show how they can be used to defend your own software from attack.

https://media.blackhat.com/bh-us-10/presentations/olleb/BlackHat-USA-2010-olleb-Hardening-Windows-Applications-slides.pdf http://www.blackhat.com/html/bh-us-10/bh-us-10-archives.html

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Protecting Your Code with Visual C++ Defenses

published by Kuling on pon., 2010-07-26 12:30

http://msdn.microsoft.com/en-us/magazine/cc337897.aspx

Kategorie:

C++

Visual Studio 2005

Czytaj dalej wpis Protecting Your Code with Visual C++ Defenses
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163 odsłony

Debugging with Visual Studio 2005/2008: Remote Debugging

published by Kuling on wt., 2010-06-01 10:15

Świetny tutorial. Polecam.

http://www.cprogramming.com/tutorial/visual_studio_remote_debugging.html

Kategorie:

Visual Studio 2005

Programowanie

Visual Studio 2008

Czytaj dalej wpis Debugging with Visual Studio 2005/2008: Remote Debugging
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196 odsłon

What happens if you allocate with vector "new[]" and free with scalar "delete"?

published by Kuling on wt., 2009-12-22 21:17

http://blogs.msdn.com/oldnewthing/archive/2004/02/04/67384.aspx

Kategorie:

C++

Visual Studio 2005

Programowanie

Retail code debugging

published by Kuling on wt., 2009-12-22 19:33

Cytat:

$vframe tells you the 'virtual frame pointer'. This is the memory address where you can find the stack frame. If the function has a true stack frame, memory will be layed out like the below table. $vframe is extremely helpful when retail debugging because it tells you where about on the stack to look for your local variables.

http://blogs.msdn.com/greggm/archive/2004/12/15/315673.aspx

Cytat:

The 32-bit x86 calling conventions

http://blogs.msdn.com/oldnewthing/archive/2004/01/08/48616.aspx

Cytat:

The following example shows the results of making a function call using various calling conventions. This example is based on the following function skeleton.

void MyFunc(char c, short s, int i, double f)
MyFunc ('x', 12, 8192, 2.7183);

http://msdn.microsoft.com/en-us/library/aa235596%28VS.60%29.aspx

Nice callstack frame.
http://blogs.msdn.com/oldnewthing/archive/2004/01/16/59415.aspx

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